Using a function to sort JavaScript objects by values

Question

So if i have an array of objects such as:

var a = [
  {
    name: "Apple",
    rank: 25
  },
  {
    name: "Cherry",
    rank: 29
  },
  {
    name: "Grape",
    rank: 15
  }
]

Is there a way to sort the values say by rank, by calling a function, i have had an attempt at it but keep getting undefined:

function sorting(obj){
    obj.sort(function(a, b){
        return a[1] - b[1];
    })
}

I am struggling to find out where i am going wrong, and am unable to find any documents on MDN regarding this.

Any help would be much appreciated, thanks in advance

Maybe you should try to sort by name return a["rank"] - b["rank"]; — Ulysse BN
– Ulysse BN, Commented Sep 11, 2018 at 22:29

ibrahim mahrir · Accepted Answer · 2018-09-11 22:39:38Z

8

Both a and b that get passed to sort's callback are the objects from the array. If you want to access their rank property you need to do a.rank not a[1]. Both a[1] and b[1] are undefined because the objects don't have a property called "1":

return a.rank - b.rank;

Example:

var arr = [{ name: "Apple", rank: 25 }, { name: "Cherry", rank: 29 }, { name: "Grape", rank: 15 }];

arr.sort(function(a, b) {
    return a.rank - b.rank;
});

console.log(arr);

Note: To reverse the order of the sorting, do this instead:

return b.rank - a.rank;

edited Sep 11, 2018 at 22:39

answered Sep 11, 2018 at 22:30

ibrahim mahrir

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Comments

Ashish Patel · Accepted Answer · 2018-09-11 22:48:29Z

One way you can solve this problem is using Quick Sort algorithm. Below I've implemented the algorithm which will print to the console your array before sort, and array after sort.

 var a = [
    {
    name: "Apple",
    rank: 25
},
    {
    name: "Cherry",
    rank: 29
},
    {
    name: "Grape",
    rank: 15
}
];

console.log(a);

function swap(firstIndex, secondIndex){
    var temp = a[firstIndex];
    a[firstIndex] = a[secondIndex];
    a[secondIndex] = temp;
}

function partition(left, right) {

    var pivot   = a[Math.floor((right + left) / 2)].rank,
        i       = left,
        j       = right;


    while (i <= j) {

        while (parseInt(a[i].rank) < pivot) {
            i++;
        }

        while (parseInt(a[j].rank) > pivot) {
            j--;
        }

        if (i <= j) {
            swap(i, j);
            i++;
            j--;
        }
    }

    return i;
}

function quickSort(left, right) {

    var index;

    if (a.length > 1) {

        left = typeof left != "number" ? 0 : left;
        right = typeof right != "number" ? a.length - 1 : right;

        index = partition(left, right);

        if (left < index - 1) {
            quickSort(left, index - 1);
        }

        if (index < right) {
            quickSort(index, right);
        }
    }
}


quickSort(a);
console.log(a);

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